Composition of hydraulic cement and polyvinyl acetate and use thereof



Oct. 16, 1962 G. w. wooDARD ETAL 3,058,520

COMPOSITION CF HYDRAULIC CEMENT AND PoLYvINYL I ACETATE AND USE THEREOFFiled July 24, 1958 INVENToRs. Geo/ge M Woodard Geo/ge A. Merk/eHTTORA/EY 3,058,520 COMPOSlTlN OF RAUUC CEMENT AND PGLYVHNYL ACETATE ANDUSE THEREOF George W. Woodard and George H. Merkle, Tulsa,

Okla., assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware Filed July 24, 1958, Ser. No. 750,628 4 Claims.(Cl. 166-31) The invention is concerned with well cementing. It isprimarily concerned with an improved well-cementing composition andmethod of cementing wells.

The obtainment of minerals in fluid form from the earths crust is besetwith a number of problems many of which are of a complex nature: afterrights of exploration and drilling are ascertained, a fluid-bearingsource must be located; a hole must be drilled into the earths crust totap the source and a casing be secured in position therein to preventsloughing of the borehole wall', a string of tubing and usually apumping system must be provided to bring the fluid to the surface; theiiow of iluid therefrom must be maintained `at a sutiiciently high rateand for a sufficiently long period of time to make the ventureeconomically feasible. These problems are particularly challenging inthe production of crude petroleum and natural gas. New compositions andmethods that increase rate of flow, insure longer producing life, orprevent contamination of the iluid sought to be produced from intrudinguids and dislodged earthen material have high utility.

The demand for gas and petroleum products is steadily increasing. As aresult thereof, drilling operations have expanded into increasinglyremote areas and diiiicultly accessible terrain which in turn hascreated more complex problems: the holes are deeper; they are oftendrilled under lakes, oceans, marshes or jungles, through shallowerlargely depleted oil strata, and through shifting unconsolidated sandsand/or fresh water or brine-producing zones which are not sealed offfrom the gas or petroleum-producing zones or from the wellbore and,therefore, continue, after completion of the well, to introduce unwantedtluids, e.g., water and brine, which also often are accompanied bydetritus and iloat sand, into the petroleum or gas Zone therebyimpairing the quality and reducing the production or cutting it ofialtogether.

Segregating or sealing off the gasand petroleumproducing zones fromzones which introduce unwanted uids together with unconsolidatedformation material continually presents new problems as additional wellsare drilled into diiterenet formations.

A slurry consisting of Portland cement and water has extensively beenused to seal oi troublesome zones and thereby prevent communicationthereof with the producing zones of the formation. The troublesome zoneor zones may be at the bottom of the well or they may be at any levelwhich has communicating channels lead ing into the petroleumorgas-producing Zone or into the wellbore directly. The usual practice, isto inject an hydraulic cement (neat cement) slurry into the well,usually between the well casing and the wall of the wellbore, at thelevel of the troublesome zones or at the bottom ot the wellbore belowthe casing if a seal is desired there.

Although a slurry of hydraulic cement and water has been of value insealing ofiunwanted fluids from gasand petroleum-producing zones, itsuse has presented a number of problems because it is lacking in certainproperties that are desirable in such a well-cementing composition.Among the properties which an hydraulic cement-water slurry lack are:ability to bond to the earthen wall of the hole; compatability withresidual slurry, mud, or brine in the wellbore or in the zone to becemented; resistance of loss of water into the formation when the slurryis subjected to the pressure necessary to force it into place, such lossof water often resulting in premature setting as well as failure to beproperly placed. The set cement also lacks shatter resistance wheneverperforations are attempted through such set cement.

These and other deciencies of-an hydraulic cementwater slurry have givenrise to a need for a better cementing material and method of sealing oiwells. In U.S. Patent 2,819,239 to Ebehard et al. there is described acementing composition and method of making and method of using such acement composition in wells which offer a number of advantages overtheretofore known compositions and methods employing such compositionsin which an hydraulic cement is an ingredient. Among such advantages areincreased bonding strength, lower liltration loss, increased toleranceto drilling muds, increased resistance to attack by sulfates -in groundwater, and greater resistance of the set cement to shattering andcracking during subsequent perforations of well casing. However, underhigh mechanical `shear at elevated temperatures, the cement of U.S.Patent 2,819,239 has tended to thicken prematurely and therefore hasrequired special care in the use thereof.

The principal object of the present invention is to provide a cementingcomposition and method of using such composition which retainsessentially all the meritorious properties of the cement of U.S. Patent2,819,239, but in addition thereto, has greater controlled thickeningtime and provides improved workability during its preparation andinjection into the well.

The improved cementing composition and the method of preparing andmethod of using such composition according to the invention will be madeclear in the ensuing description and is defined in the appended claims.

The improved well-cementing composition of the invention consistsessentially of an aqueous slurry of an hydraulic cement and a polyvinylacetate polymer latex. Wetting, antifoaming, and antifreeze agents maybe adrrn'xed therewith, if desired, to impart properties peculiar to thepresence of such additives. The dispersant preferred is a non-ionicsurfactant, e.g., octyphenol or disecondary-butylphenol condensed withan average of 10 or 12 moles of ethylene oxide.

The drawing is a schematic representation of an oil well during thatstage of squeeze cementing a well according to the method of theinvention which exists just after the hydraulic cement-polyvinyl acetateslurry has been pumped into the well tubing but prior to its injectionthrough perforations in the casing at the zone of intruding fluids. Thelocation of the squeeze cement positioned in the intrusion zone issuggested by a broken line.

Referring to the drawing in greater detail there are shown `surfacecasing 10 extending to casing shoe 11 at a depth of 10,608 feet andinterior thereto casing 12 extending from ground level to a depth of21,007 feet. Set cement poured at the time casing 10 was set in the wellis shown in item 131. Casing '12 shows perforations 14 therein openinginto intrusion zone 16 between the levels of 10,648 and 10,724 feet. Ashort distance below intrusion Zone 16 in the wellbore at a level of10,730 feet is bridge plug 17 positioned therein as a preparatory stepin cementing oif zone 16 in accordance with the invention. Below plug 17is Shown pay zone 18. Tubing 19 extends to a depth a yshort distanceabove perforations 14, and together with casing 12 denes annulus 20therebetween. Packer 21 is shown in position at the lower end of tubing19 in annulus 20'. In the lower part of casing 12 there is shown setcement 22 from a prior cementing job. The space between the Wellborewall and casing 12 contains cement 23 positioned there when 3 the casingwas placed in the well. Below 17 is drilling mud 24 above which is water26. Above 26, which follows water 26 into the formation during theccmenting operation, is cement-latex slurry composition 28 of theinvention. Item 30 is the first portion of ush water which follows theslurry during the cementing operation.

Item 32 represent-s 'a small amount of water allowed to enter annulus 20before packer 21 was set to aid in holding the packer in place.

Item 34 shown `by a dotted outline represents the suggested position ofpancake-like cement composition of the invention after it is positionedin the well at the close ofthe treatment.

To prepare the composition of the invention, an hydraulic cement isadmixed with a plyvinyl acetate emulsion latex. The practice of theinvention requires only the hydraulic cement, the polyvinyl acetatelatex, and

water. Usually the latex is tirst diluted with water before admixing itwith the hydraulic cement. The preferred practice of the invention is toadmix a small amount of a dispersant Vwith the diluted latex prior toadmixing it with the hydraulic cement. A small amount of an antifoamingagent and/or an antifreeze agent may be advantageously added to thelatex admixture thus made with agitation. For convenience, they areusually added prior to admixing with the hydraulic cement. Mixing iscontinued for from 10 to 40 minutes or until a substantially homogeneousmixture is obtained. Any suitable mixing apparatus provided withadequate stirring is satisfactory for preparing the composition of theinvention.

Table I =below sets out the operable and the preferred limits of theingredients of the composition of the invention in parts by Weightlbased upon 100 parts of an hydraulic cement.

Table I Ingredients Operable Preferred Y limits limits Essentialingredients:

Hydraulic cement. 100 100 Water 32-72 40-58 Latex solids. 2. -25 3-15Optional additives:

Wetting agent (surfactant) 0. 2-1. 5 0. 3-1. 0

Antzlreeze agent 0. 25-1. 6 O. 5-1. 0

Antioamingragent 0. 01-0. l 0. O15-0. 075

The latex is an aqueous emulsion or suspension system comprisinghomopolymer particles varying from 0.3 to microns but usually between land 5 microns in diameter. The percent latex `solids are generallybetween 50 and 60 percent by weight of the emulsion, about 55 percent-being most common. The viscosity at C. may be between 600 and 3000centipoises but is more 'commonly -between 1200 and 1800 centipoises.The specic gravity at 25 C. is usually about 1.1, the weight per gallontherefore being about 9.2 pounds. Methods of preparing polyvinyl acetateemulsions or suspensions are Well known. The monomer requires thepresence of a protective colloid to prevent hydration dur ing the earlystages of the polymerization. To prevent this hydration, 1 to 5 percentof polyvinyl alcohol as a protective colloid is usually added. A methodof preparing a polyvinyl acetate emulsion consists essentially ofadmixing the ingredients set out in the recipe in Table II below.

Table II Ingredients: Parts by weight Emulsier to reduce surface.tension 0.40 Polyvinyl alcohol 1.25 K2S2O4 0.10 NaHCO3 0.05 Vinylacetate 55.00 Water suiiicient to malte 100.00.

Usually part of the water is placed in a glass-lined kettle under reiluxprovided with continuous agitation and a heating means. To the water areadmixed ythe polyvinyl alcohol, KZSZOS (the initiator or catalyst),NaHCO3 (as a buffer), and a small part of the vinyl acetate, say 5 partshy weight. The kettle is heated and when the temperature reaches about70 C., polymerization begins. The balance of the water is usually addedat this time and when .the temperature is about 72 C. the balance of thevinyl acetate is admixed gradually. The temperature is held below C.Polymerization is usually completed after about 2 hours. A branched andcrosslinked polymer is obtained by this method which imparts addedtoughness to the latex particles when dry. If desired, a comparativelylarge amount of polyvinyl alcohol may be employed to form a polymercontaining substantial amounts of polyvinyl alcohol that serve as a sortof nuclei in the polymer.

The emulsier employed in the preparation of polyvinyl acetate latex ispreferably of the anionic type surfactant. Anionic surfactants contain apredominant negative ionizable group which will migrate in a solutioncontaining an anode or positive pole, toward such pole. A particularlysatisfactory surfactant of the anionic type employed is of the alkylarylsulfonate class. Other examples of anionic surfactants are (l) fattyacid, rosin acid, and naphthenic acid soaps,i(2) sulfated ethers andamides, (3) sulfonated esters and amides, and (4) sul-fated oils andesters. Nonionic surfactants may be employed in the production ofpolyvinyl acetate latices, however, either singly or in conjunction withanionic. Non-ionic surfactants do not contain an ionizable group andhave no electrical charge in the polymerizable mixture. Examples ofnon-ionic surfactants are (l) alkyl and alkylaryl ethers and thioethersand (2) esters and amides and, more specically, the condensation productof ethylene oxide and octyl phenol mentioned above. Generally speaking,an emulsier useful in preparing the polyvinyl acetate should reduce thesurface tension of water 'from between 72 and 30 dynes per centimeter ata concentration of less than 0.01 percent. It must produce relativelylarge and stable micelles and lbe unreactive with the ingredients in themonomeric and polymerizing mixture.

The hydraulic cement employed may be any of the cements referred to asPortland cement or aluminous cement. For example, A.S.T.M. Types I, 1I,III, and IV designated C-l50 to C-l52, respectively, part IIII pages l-Sof A.S.T.M. Standards (1952) may be employed in the invention.

Latex-cement compositions useful in cementing off zones in a formationtraversed by a well and useful in positioning casing in Wells accordingto the invention, together with compression strength values, are set outin Tables IH, IV, V, VI and VII. In preparing the composition of TableIII, polyvinyl acetate latex was diluted with water and Portland cementadded particularly slowly thereto to obtain a smooth slurry. 'Inpreparing the composition of Table IV, a dispersant was admixed with thediluted latex prior to admixing with Portland cement. In preparing thecompositions of Tables V, VI and VII, both an antifoam and antifreezeagent as well as a dispersant were admixed with the diluted latex priorto admixing with Portland cement. The Portland cement was addedrelatively rapidly in the presence of the dispersant showing thebeneficial effect of presence thereof.

The compression strength was determined according to the procedure setout in A.S.T.M. Standards, part III, pages 119-125, Designation C-l09-52entitled Compression Strength of Hydraulic Cement Mortars.

The tables show both the parts by weight of the ingredients -based onparts by weight of Portland cement and the percentage composition byweight of the slurry and of the set or dry latex-Portland cementcomposition.

Table III tion. The latex-cement slurry compositions were pre'- paredwherein the ingredients were admixcd in the same Parts by Percentagecom- Compression amounts 1n each of the compositions as in those shownin 'lltyof Position 0f- Stfength PS-1 Table V except that the percentageof water was varied. Ingredients bea on s t 5 A compression strength wasrun on each of the composil parts o cedry Pom Smm, ment 80, F. 120., Etions thus prepared. The mgredlents 1n the compositions nud equipoandthe compression strength after 24 hours setting time cement smo at 80 F.are shown in Table VI below. The results ob- P t1 d l XSTM tained inTable V are repeated in Table VI Ifor ready Ol 2111 Cement; 1 P'pype 1 1100.00 06.29 compauson' o yviny aceta e em sion 1 7. 09 2 4. 71 Table VIWater 40. 60 29. 00

153. 69 100.00 100.00 1,002 a, 700 Parts by welght Percent- Compl-esAmt. in based on age sion loonsisnng of 55 percent latex sends.Insredlents lbs. 100 parts Composi- Strength, 2 Since the latexconsisted of 55 percent latex solids, the latex solids by Weight tion op.s.i added were 2.59 percent of the slurry and there was added by wayof 0f any slurry the latex 2.12 percent of water, making a total of31.127 percent water Cement present.

An examination of Table III shows that a cement of 2O Portland cernenlt1, 034 100.00 73.15 2,348 high compression strength can -be madeemploying an fjvleuslflf:21:: 7g: 0 2 gj g? ajg hydraulic cement,polyvinyl acetate lateX, and water acoltytglycol.-- 4.5 0.44 0.33cordine to the invention wfterata1-- :132131: 2931?) 2313i L :11T-

Table l V Toter weight 1, 413.0 130. e6 25 Water added plus water fromlatex 325. 0 3l. 34 Parts by Percentage com- Compression vreight ofposition ostrength p.s.i.

slurry Water added 4...-. 442 42.74 Ingredients based on 'Water addedplus 100 parts Set cex 4 482.6 45. 93 dry Port- Slurry ment 80 F. 1207 Frand com po- Portland cement 1, 034.0 100. 00 cement sition PVA emulsion73. 2 7.09 Ethylene glyco 9.0 0.87 Polyglyc0l 4. 5 0. 44 Portland cementASTM Antifoamer. 0. 2 0. 02 Type I 100. 00 66. 20 92.96 Water added.-708. 0 68. 50 Polyvinyl acetate emul sion 1 7.10 24. 70 6.60 35 Totalweight 1,829.0 176.92 Polyglycol (dispersaut) 0.30 0.80 0.44Wateraddedpluswaterfrom Water 29. S0 latex 741. 0 71. 70

1 Consisting of 55 percent latex solids. 1 PVA= Polyvinyl acetateemulsion, 55 percent total solids. 2 Since the latex consisted of 55latex solids, the latex solids 40 2 Solids only equal 3.9.

percent added were 2.58 percent of the slurry and there was added by wayof the latex 2.13 percent of water making a total of 81.93 percent Waterpresent.

An examination of Table IV shows that a dispersant may be employed inthe practice of the invention to facilitate the mixing thereof Withoutappreciable effect upon the compression strength of the composition thusprepared.

3 Solids only. 4 Same as Table V.

The slurries prepared according to the invention as lshown by Table VIwere readily pumpable and retained their fluid properties for asuiciently long period to be injected into a well and positioned thereinin a well-cementing operation. The compression tests of thecompositions, as set out in Table VI, show that between Table VPercentage compo- Compression Parts by sition strength p.s.i. weight ofIngredients Amount in slurry based pounds on 100 parts Set dry PortlandSlurry cement 80 F. 120 F.

cement composltion Portland cement ASTM Type L 1 1, 034 100. 00Polyvinyl acetate emulsion 73. 3 2 7. 09 Ethylene glycol 9.0 0.87Wetting agent (polyglycol) 4. 5 0. 44 Antifoam agent (silicon type) 0. 2O. 02 later added 442. 0 42. 74

Total Weight 1,503.0 151.16 Water added plus water from latex 482. 6 45.93 30. 41 Total solids weight (without water) 1,121

(contained 45 percent Water) Water in the amount of 2.11 percent by bythe latex making a total of 30.41 percent water.

31.43 and 71.7 parts by weight of water based on 100 parts by weight ofdry Portland cement containing 3.9

parts by weight of polyvinyl acetate iatex solids are sufciently highyfor well cementing operation. When less than about 32.0 parts water,based on 100 parts by Weight of hydraulic cement (about 23 percent), wasused, the

slurry composition was too thick to be readily pumped'.

s When more than about 72 parts by weight (about 40.6 percent) waterwere used, the slurry tended to stratify and become non-homogeneous.However, the higher proportions of water tend to lower the compressionstrength and the lower proportions tend to unduly thicken the slurry. Itis recommended that the Water be between 40 and 58 parts based on 100parts by weight of dry cement. A series of runs was made to show theeffect on compression strength of the set cement latex composition ofthe invention which resulted when the amount of latex solids was variedin the composition. The amount of ethylene glycol added was increasedproportionately to the latex solids present to maintain the ratio ofTable V and the amount of water added was decreased as the latex wasincreased because with the increased latex solids a measurable amount ofwater was added. The total amount of water was held about 30.4 percentof the wet composition or slurry. In runs 1, 6 and 8 no latex was used.These runs were for comparison purposes. Runs 2 to 5, 7 and 9 illustratethe practice of the invention. The results obtained by increasing thelatex solids from to 5.6 percent by weight at 80, and 2.6 percent at 120and 200 F. are set out in Table VII below.

An examination of Table VII shows` that the compres sion strength aftera setting period of 24 hours at 80 F. for each amount of latex solidsused was but little less than when only Portland cement was used. Thetable shows that at advanced temperatures, the compression strength ofthe latex-Portland cement composition of the invention was considerablyless than that of Portland cement alone. However, the compressionstrength was still suiiiciently high for well cementing operations.

Another series of runs was made in which the amount of a wetting agentwas employed in varying amounts. The composition of the latex-cementslurry was the same as that given in Table V except a diierent wettingagent was used. The wetting agent in this series of runs consisted ofthe condensation product prepared by condensing di-secondary-butylphenoland ethylene oxide in a molar ratio of l of the di-secondary phenol tol0 of the ethylene oxide. The ingredients Were added to the mixer withina short time without particular precautions to prevent lumping.Compression strengths were run on each of the samples after a 24 hourdrying time at 80 F. The results are set out in Table VIII below.

1 Latex coagnlated and did not mix in properly.

An examination of the results set out in Table VIII shows that at least0.2 percent wetting agent is required to disperse the latex smoothlyunless the ingredients are added slowly accompanied by especial stirringprecautions to prevent lumping. Further examination shows that butlittle improvement in compression strength resulted when more than 0.5percent wetting agent was employed but no appreciable adverse effectcould be seen by employing as much as 4 perce-nt.

A further series of runs was made for the purpose of comparing the iiuidloss of cement slurries prepared according to the invention and thoseprepared according to U.S. Patent 2,819,239. The fluid loss wasdetermined according to the American vPetroleum Institute Standard'Field Procedure for Testing Drilling Fluids (tentative) API RP 29, 3rdEdition (May, 1950). The slurry composition prepared according to theinvention was that set out lin Table V above. The composition preparedaccording to U.S. Patent 2,819,239 consisted of a substantiallyhomogeneous mixture of: 55 gallons of Water, 0.5 gallon of octylphenolcondensed with 10 moles of ethylene oxide, 6.7 gallons of an internallyplasticized vinylchloride copolymer emulsion, and 0.8 ga'llon ofethylene glycol admixed with 1034 pounds (ll sacks) of Portland cement,ASTM Type I. A comparison of the results of the iiuid loss isdeterminable by referring to Table IX below.

lLatex-cement became excessively thick and was barely pumpable: theiluid loss values, therefore, could not be accurately determined.

2 Extrapolated.

A further series consisting of runs 2l, 22, and 23 was made to show theworkability of the latex-cement composition of the invention incomparison with conventional neat Portland cement and with the improvedlatex-Portland cement composition of U.S. Patent 2,819,239. The test ofworkability of 'the cementing composition was carried out in accordancewith Schedule 5 of the American Petroleum Institute Recommended Practicefor Testing Oil Well Cements API RP 10B, 5th Edition (May 1956). Thetest simulates a cementing operation of an 8000 foot well having abottom hole temperature of 125 F. Briefly the test comprises subjectingthe cement slurry to increments of pressure and temperature for 55minutes and then holding the cement slurry at these conditions withagitation until the viscosity reaches poises. This viscosity is usedbecause a higher viscosity is considered too thick to pump. The resultsof the test are stated as thickening time which is the length of timewhich elapses between the beginning of the pressure and temperativeincrements and the time the viscosity is 100 poises. The neat Portlandcement composition, run 21, consisted of 100 grams of Portland cementASTM Type I and 46 grams of water. The latex-Portland cement compositionof U.S. Patent 2,819,239 was that set out in the paragraph precedingTable IX above. The polyvinyl acetate-lateXPortland cement slurry of theinvention was that set out in Table V above. Y

The results of the thickening tests set out in Table X 9 show that thelatex-cement composition of the invention was about 0.9 that of neatcement whereas the latexcement composition o U.S. Patent 2,819,239, hada thickening time which was less than 0.6 that of neat cement.

An example of cementing an oil well according to the invention is asfollows:

Stage 1.-A 400-gallon batch of the polyvinyl acetate latex-cement slurryof the invention was prepared by admixing 212 gallons of water, 36.5gallons of a polyvinyl acetate emulsion (55 percent total solids havinga particle size between l and microns), 1.9 gallons of di-secbutylphenolcondensed with l0 moles of ethylene oxide, and 1.4 quarts of siliconetype antifoamer in a 50G-gallon paddle mixer and continuing to mix for15 minutes. Then 4512 pounds (48 sacks) of Portland cement were addedslowly to the contents to the paddle mixer and stirring continued for aperiod of 30 minutes.

An oil well in the Headlee Pool, Ector County, Texas, which is shownschematically in the drawing was selected to be cemented according tothe invention. Zone 18 at a level of about 11,000 feet in a Pennsylvaniastratum was producing in a unitized eld. It was desired to cement ott aDevonian stratum at a level of between 10,648 and 10,724 to whichreference is made as intrusion zone 16. It was necessary that a squeezecement job be able to withstand a pressure of about 7000 p.s.i.Preparatory to cementing oft according to the invention, bridge plug 17was positioned in the well as shown and pertorations 14 made throughcasing 12 at the intrusion zone. Packer 21 was positioned in an opencondition, not as shown, in annulus 20. Drilling mud 24 resting oncement 22 from a previous cementing job was in the wellbore at the startof the cementing operation. To begin the treatment of the well, tenbarrels of water were rst pumped down tubing 19, two barrels of which,indicated by numeral 32, were forced up into annulus 20 before closingpacker 21, and eight barrels remained above the level of drilling mud 24in casing 12 and in tubing 19. The 400 gallons (9.5 barrels) oflatexcement composition 28 prepared as described in the paragraph above,were then pumped down tubing 19 tollowed by twenty barrels of ush water30. The pressure in casing 12 at the well head was raised to 1800p.s.i., the pump stopped, and the pressure held here for about minutesand then raised to 4800 p.s.i. to force the latex-cement compositionthrough perforations 14 and against the area of the formation into thearea designated 34, defined by a dotted outline. The pressure, however,bled oi slowly indicating that there had not been a complete sealing offof the formation.

Stage 2 A 5 OO-gallon batch of the latex-cement composition was made upof the same proportions used in the 400-gallon batch prepared and usedin Stage 1. This SOO-gallon batch Was forced into the well and ushedback into the formation similar to the procedure used in Stage 1 exceptthat the Iinal pressure was 5800 p.s.i. The pressure did not hold butslowly bled oit indicating again that a complete seal in the formationhad not yet been accomplished.

Stage 3.-A Z50-gallon batch of latex cement composition was madefollowing the procedure used in Stages 1 and 2 except that the iinalinjection pressure was raised to 7000 p.s.i. When the pump was stoppedthe pressure did not drop, that is, there was no bleeding 01T into theformation thus showing that a good seal had been made. The pressure wasreleased and bridge plug 17 drilled out. The well was then put back intoproduction, producing fluids only from below the 11,000 foot level.

The polyvinyl acetate-hydraulic cement composition of the inventionoffers a number of advantages over neathydraulic cement now employed inoil well ce-menting. The cement composition of the invention bonds tooil or brine-wet walls, or walls having a sheath of residual drillingmud adhering thereto; it tolerates relatively large amounts ofcontaminants such as mud, when set, it is resistant to shattering duringsubsequent perforations of the casing; it is more resistant generally to.chemical attack by dissolved materials in the oil and water, eg.,sulfur compounds.

The polyvinylacetate-hydraulic cement of the invention olters Vtheadvantages of greater workability and greater permissible time betweenmixing and placing in the well over the latex-cement composition of U.S.Patent 2,819,239. A particularly import-ant advantage of the compositionof the invention over other cementing compositions including that ofU.S. Patent 2,819,239 is the improved iluid loss control thereover atelevated temperatures.

Having described the invention, what is claimed and desired to beprotected by Letters Patent is:

1. The process or cementing a well traversing an earthen formation wihchcomprises positioning therein a settable slurry comprising by weightparts of Portland cement, between 2.5 and 25 parts of polyvinyl acetatelatex solids, and between 35 and 65 parts of water.

2. The process of cementing oit intruding iiuids from fluids sought tobe produced from an earthen formation traversed by a well which consistsof cementing oit said intruding iiuids from access to the uids sought tobe produced by positioning at the place of intrusion a settable slurryconsisting essentially by weight of 100 parts of Portland cement,between 2.5 -and 25 parts of polyvinyl acetate latex solids, between 0.2and y1.5 parts of a nonionic surfactant, and between 35 and 65 parts ofwater.

3. The process of cementing oli intruding fluids from fluids sought tobe produced from an earthen formation traversed by a ywell whichconsists of cementing oft said intruding fluids from access to the udssought to be produced by injecting at a pressure greater than thatexerted by the intruding fluids at the place of intrusion a settableslurry consisting essentially of a mixture of 100 parts of Portlandcement, between 40 and 58 parts of water, between 3 and 15 parts ofpolyvinyl `acetate latex solids, up to 1 part of an antifreeze agent,and up to 0.075 part of an antifoami-ng agent.

4. The process of claim 2 wherein said settable slurry is prepared byadmixing said non-ionic surfactant with an aqueous emulsion of saidpolyvinyl acetate, said emulsion comprising between 50 and 60 percenttotal latex solids having a particle size `of between l and 5 microns indiameter, land admixing the so treated emulsion with said cement.

References lCited in the tile of this patent UNITED STATES PATENTS2,733,995 Robinson Feb. 7, 1956 2,757,737 Schremp Aug. 7, 1956 2,819,239Eberhard Jan. 7, 1958 2,865,876 Scott Dec. 23, I1958 2,868,753 MorganJan. 13, 1959 FOREIGN PATENTS 562,859 Great Britain July 19, -194'4635,486 Great Britain Apr. l2, 1950 OTHER REFERENCES Payne, P\a.int, Oil& Chem. Review, October 22, 1953, pages 16,-18, and 44.

1. THE PROCESS OF CEMENTING A WELL TRAVERSING AN EARTHEN FORMATION WHICHCOMPRISES POSITIONING THEREIN A SETTABLE SLURRY COMPRISING BY WEIGHT 100PARTS OF PORTLAND CEMENT, BETWEEN 2.5 AND 25 PARTS OF POLYVINYL ACE-